1. Field of the Invention
The present invention relates to the manufacture of metal turbomachine blading, more particularly of components having internal cavities and holes or orifices allowing these cavities to communicate with the outside of the blading.
2. Description of the Related Art
Such blading is generally manufactured by casting individual blading components each constituting a blading sector, using a lost wax casting technique that is well known per se. This technique goes through a stage of producing a model in wax or some other equivalent material which comprises an internal component that forms a casting core and features the cavities of the blading. In order to form the model, use is made of an injection mold for the wax in which the core is placed and into which the wax is injected. The wax model is then dipped several times into casting slip consisting of a suspension of ceramic particles in order to produce a shell mold. The wax is eliminated and the shell mold is baked. The blading is obtained by casting molten metal which then occupies the voids between the interior wall of the shell mold and the core.
In a turbomachine low-pressure guide vanes stage, some of the blades or vanes have an internal cavity and a series of holes causing this cavity to communicate with the outside of the blade. This cavity and this series of holes allow temperature detection probes, known as EGT (exhaust gas temperature) probes, to be fitted. By way of example, for low-pressure guide vanes of a turbomachine of the type found in the prior art, comprising 18 blading segments or sectors, one blade in each sector comprising 8 blades is provided with an internal cavity and with a series of holes.
The temperature probes in this particular region of the turbomachine are used to monitor correct operation and engine wear.
Using the current technique, the cavity in this blading that is to accept a temperature probe is produced by fitting cores equipped with upper and lower tenons which, when the metal is cast, form orifices in the exterior platform and in the interior platform of the component; the orifice in the exterior platform is intended to accept or be in communication with the temperature probe, while the orifice in the interior platform serves only to hold the core in place while the metal is being cast and therefore requires the fitting of a blanking plate, which is brazed on during the finishing operations on the blading sector.
The holes providing communication between the cavity of the airfoil of the blade that accepts the probe and the outside of the blading are produced by drilling/machining (notably by spark erosion or electrical discharge machining (EDM)) after the component has been cast.
This approach therefore entails an additional operation which, furthermore, generates a scorched region around the hole where the mechanical properties are inadequate.